
\begin{tikzpicture}[scale=.5]
  \coordinate[label=above left:$B$] (B) at (0,0);
  \coordinate[label=above:$A$] (A) at ({5*sqrt(3)},3);
  \coordinate[label=below:$C$] (C) at ($ (A)!1! 60:(B) $);
  \coordinate[label=above:$U$] (U) at (0,3);
  \coordinate[label=below:$V$] (V) at (0,-6);
  \coordinate[label=below:$W$] (W) at ({5*sqrt(3)},-6);
  \pic[mark angle={green}{3mm}{1}] {right angle=B--U--A};
  \pic[mark angle={green}{3mm}{1}] {right angle=C--V--B};
  \pic[mark angle={green}{3mm}{1}] {right angle=A--W--C};
  \draw[thick] (-.5,3) -- (9,3) node[right] {$l_1$}
    (-.5,0) -- (9,0) node[right] {$l_2$}
    (-.5,-6) -- (9,-6) node[right] {$l_3$};
  \filldraw[opafill=blue] (A) -- node[above] {$c$} (B)
    -- node[above] {$c$} (C) -- node[left] {$c$} cycle;
  \draw[dashed] (U) -- (V) (A) -- (W);
  \fill[opafill=cyan]
    (A) -- (B) -- node[left] {$a$} (U)
      -- node[above] {$\sqrt{c^2 - a^2}$} cycle
    (B) -- (C) -- node[below] {$\sqrt{c^2 - b^2}$} (V)
      -- node[left] {$b$} cycle
    (A) -- (C) -- node[above right, rotate=15] {$\sqrt{c^2 - (a+b)^2}$} (W)
      -- node[below, sloped] {$a + b$} cycle;
\end{tikzpicture}
